Hi Topper
Unfortunately, it sounds like Drew is right, I am informed by my son, a part P ELECSA registered spark, who rips a lot of this stuff out, that aluminium cables were in common use 30/35 years ago, apparently, the cable without earth was used earliest.
He also told me that where aluminium cable has to be used now, the conductor core sizes for current rating have been greatly increased since then to account for the malliability of the metal.
So Yes, rewire ASAP Im affraid, if you need any advice you can always ring young Darren on 07738232852 he will be pleased to help, even if its just make sure you dont get ripped off on the price of a rewire.